The present invention relates generally to systems for reducing impulsive noise, and more particularly to a system for effectively reducing impulsive noise in transmitted audio signals, such as music.
In general, if there are damaged parts or if extraneous substances such as dust exist on the surface of the record disc, an impulsive noise commonly called a "popping noise" becomes admixed with the reproduced audio signal.
In a conventional record disc reproducing apparatus, however, there is no circuit for reducing this impulsive noise. When a record disc with a damaged sound groove or a record disc with dust adhering thereto is reproduced (played), the impulsive noise is reproduced at the same time to produce an unpleasant to the sensation listener.
However, when this impulsive noise was examined, it was found that, its frequency differs depending upon the nature of the damage to the sound groove and the dust on the record disc. The incidence noise frequency ranges from a low value in the order of one occurrence in the period (1.8 seconds) of one revolution of the record disc to a high value of the order of several occurrences per second, in the case of a record disc having damage within the limit of hearing. In addition, the level of the peak of an impulsive noise is considerably higher than the average level of an ordinary music signal.
In contrast, in general music, the ratio of the peak signal level relative to the average signal level is not high. However, a trumpet sound is an example of a signal wherein this ratio is relatively high. In the signal of this trumpet sound, while the ratio of the peak level relative to the average level is high, the number of cycles of repetition of the peak is of the order of 500 to 1,000 in one second. This is extremely great in comparison with the above mentioned frequency of the impulsive noise.